[jdk8u-dev] RFR: 8253797: [cgroups v2] Account for the fact that swap accounting is disabled on some systems [v4]

[Jonathan Dowland]

> This is a clean backport of 8253797 (via 11u) for jdk8u-dev for cgroups v2 support.
> 
> The changed files are exercised by the jtreg test `TestSystemMetrics.java` which passes on my cgroups v2 system.

Jonathan Dowland has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 24 commits:

 - 8253797: [cgroups v2] Account for the fact that swap accounting is disabled on some systems
   
   Backport-of: 669361117d30c9904813b6f728714f8d6abe8484
 - 8253939: [TESTBUG] Increase coverage of the cgroups detection code
   
   Backport-of: 42fc15899115ca61151bbee96b5580d4e4252beb
 - replace use of Optional.isEmpty
 - 8245543: Cgroups: Incorrect detection logic on some systems (still reproducible)
   
   Backport-of: 2bbf8a2a964a64d88298a3dd184459af506e58ed
 - Severin's test fixes. Thanks!
 - Replace log_warning with tty->print_cr
 - 8253435: Cgroup: 'stomping of _mount_path' crash if manually mounted cpusets exist
   
   Backport-of: 0054c15f60cce6470be05d29bfacbdb74cfb7bc9
 - 8252359: HotSpot Not Identifying it is Running in a Container
   
   Backport-of: 76f0588aaf265439a589cceb924e3ea9d3fda8f1
 - replace log_trace with tty->print_cr
 - 8278951: containers/cgroup/PlainRead.java fails on Ubuntu 21.10
   
   Reviewed-by: sgehwolf
   Backport-of: 35172cdaf38d83cd3ed57a5436bf985dde2d802b
 - ... and 14 more: https://git.openjdk.org/jdk8u-dev/compare/362cf762...7c0dab20

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Changes: https://git.openjdk.org/jdk8u-dev/pull/185/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=185&range=03
  Stats: 1618 lines in 20 files changed: 1289 ins; 145 del; 184 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/185.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev pull/185/head:pull/185

PR: https://git.openjdk.org/jdk8u-dev/pull/185